Various systems and methods are described for regulating the charge pressure pboost of a supercharged internal combustion engine. The engine may have at least one cylinder, and may further include an intake system for the supply of charge air to the at least one cylinder, and an exhaust-gas discharge system for the discharge of the exhaust gas from the at least one cylinder. The system may further have at least two compressors arranged in series in the intake system, of which a first compressor serves as a low-pressure stage and a second compressor serves as a high-pressure stage.
Control of such a system can be particularly challenging, especially when the second compressor is arranged downstream of the first compressor and there is a first bypass line provided which branches off from the intake system between the first compressor and the second compressor and which opens into the intake system downstream of the second compressor, where a first control element is arranged in the first bypass line. For example, control with a single pressure target via two different turbochargers in series might become difficult in an overlap RPM region (e.g., 2000-3000 rpm) where the high pressure turbocharger is losing efficiency and the low pressure turbocharger is gaining presence. A change in actuator setting on the first one might result in an effect on pressure opposite to what is targeted caused by the second one. (For example, opening of bypass to reduce boost could result in increase of pressure due to higher exhaust energy deviated from the high to low pressure turbine.
Thus, in one approach a first setpoint value for the pressure pinter-stage, set in the intake system between the first compressor and the second compressor is predefined, and the pressure pinter-stage in the intake system between the first compressor and the second compressor is determined. Then, using the pressure difference Δp1=pinter-stage,set−pinter-stage, in a first regulation loop, the drive power of the first compressor is varied (e.g., via a wastegate or variable geometry adjustments) in order to regulate the pressure pinter-stage, a second setpoint value for the pressure pboost, set in the intake system downstream of the second compressor is predefined. The pressure pboost in the intake system downstream of the second compressor is then determined, and using the pressure difference Δp2=pboost, set−pboost, in a second regulation loop, the drive power of the second compressor is varied (e.g., via a wastegate) in order to regulate the pressure pboost.
In another example, a method comprises adjusting each of two wastegates, a variable turbine geometry, and a downstream compressor bypass valve to regulate engine boost pressure as a function of a first setpoint value for pressure between compressors and a pressure difference in a first regulation loop, a second setpoint value for pressure downstream of multiple compressors, and the pressure difference in a second regulation loop.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.